The present invention relates generally to photovoltaic materials and manufacturing method. More particularly, the present invention provides a method and structure for uniform thermal treatment of thin film solar cells. Merely by way of example, embodiments of the present invention include a method and structure for controlling convective flows during reactive thermal process for forming a photovoltaic film stack of solar cells, but it would be recognized that the invention may have other configurations.
From the beginning of time, mankind has been challenged to find ways of harnessing energy. Energy comes in forms such as petrochemical, hydroelectric, nuclear, wind, biomass, solar, and more primitive forms such as wood and coal. Over the past century, modern civilization has relied upon petrochemical energy as an important energy source. Petrochemical energy includes gas and oil. Gas includes lighter forms such as butane and propane, commonly used to heat homes and serve as fuel for cooking. Gas also includes gasoline, diesel, and jet fuel, commonly used for transportation purposes. Heavier forms of petrochemicals can also be used to heat homes in some places. Unfortunately, the supply of petrochemical fuel is limited and essentially fixed based upon the amount available on the planet Earth. Additionally, as more people use petroleum products in growing amounts, it is rapidly becoming a scarce resource, which will eventually become depleted over time.
More recently, environmentally clean and renewable source energy has been desired. An example of a clean source of energy is hydroelectric power. Hydroelectric power is derived from electric generators driven by the flow of water produced by dams such as the Hoover Dam in Nevada. The electric power generated is used to power a large portion of the city of Los Angeles in California. Clean and renewable sources of energy also include wind, waves, biomass, and the like. That is, windmills convert wind energy into more useful forms of energy such as electricity. Still other types of clean energy include solar energy. Specific details of solar energy can be found throughout the present background and more particularly below.
Solar energy technology generally converts electromagnetic radiation from the sun to other useful forms of energy. These other forms of energy include thermal energy and electrical power. For electrical power applications, solar cells are often used. Although solar energy is environmentally clean and has been successful to a point, many limitations remain to be resolved before it becomes widely used throughout the world. As an example, one type of solar cell uses crystalline materials, which are derived from semiconductor material ingots. These crystalline materials can be used to fabricate optoelectronic devices that include photovoltaic and photodiode devices that convert electromagnetic radiation to electrical power. However, crystalline materials are often costly and difficult to make on a large scale. Additionally, devices made from such crystalline materials often have low energy conversion efficiencies. Other types of solar cells use “thin film” technology to form a thin film of photosensitive material to be used to convert electromagnetic radiation into electrical power. Similar limitations exist with the use of thin film technology in making solar cells. That is, efficiencies are often poor. Additionally, film reliability is often poor and cannot be used for extensive periods of time in conventional environmental applications. Often, thin films are difficult to mechanically integrate with each other. These and other limitations of these conventional technologies can be found throughout the present specification and more particularly below.
As an effort to improve thin film solar cell technology, one or more processes of manufacturing an advanced CIS and/or CIGS based photovoltaic film stack on sized substrates with planar, tubular, cylindrical, circular or other shapes are introduced. There are various manufacturing challenges in forming the photovoltaic film stack, such as maintaining structure integrity of substrate materials, controlling chemical compositions of the ingredients in one or more precursor layers, carrying out proper reactive thermal treatment of the one or more precursor layers within a desired gaseous environment, ensuring uniformity and granularity of the thin film material during reactive thermal treatment, etc. Especially, when manufacturing the thin film based solar cell on large sized substrate, temperature uniformity across whole substrate surface is desired. While conventional techniques in the past have addressed some of these issues, they are often inadequate in various situations. Therefore, it is desirable to have improved system and method for processing thin film photovoltaic devices on planar or nonplanar shaped, fixed or flexible substrates.